1. Field of the Invention
The present invention relates to a connector device to connect the end of a cylindrical rod or a cylindrical wire. In particular, the present invention relates to a connector to connect the end of the cylindrical rod or wire so that the rods or wires are connected therein in end-to-end relationship.
2. Prior Art
The use of cylindrical or sucker rods is well known in underground wells to actuate a pump located in an underground well bore of a well. A series of sucker rods connected together in end-to-end relationship forms a string which extends down into the well hole. The string is connected to a pump at one end and to a reciprocating mechanism at the surface or well head in order to actuate the pump.
While at one time steel sucker rods were common, synthetic materials, such as fiberglass or other synthetic resins are being increasingly used. Fiberglass rods are advantageous because they are lighter than metal, withstand corrosive effects better than metal and have greater elasticity than metal.
The individual rods are connected together by metal connectors which are generally elongated members having an axial receptacle. The connector will typically have an opposite threaded end so that a pair of connectors may be secured together. The sucker rod may be connected to the connector through use of an adhesive which will bond to the rod.
Various designs have been suggested to produce a good bond and attachment between the rod and the end fitting.
Prior designs include Anderson et al. (U.S. Pat. No. 4,653,953), Parsons et al. (U.S. Pat. No. 4,433,933) and McKay (U.S. Pat. No. 4,401,396). A series of wedge or partial cone-shaped recesses extend from the receptacle into the body of the connector.
In order to make the attachment, an initially flowable adhesive is placed in the receptacle of the connector. A rod is then inserted into the receptacle, the adhesive fills the void space in the wedges or partial cone-shaped cuts. The adhesive will cure becoming a solid and will adhere to the rod. The solid adhesive is bonded to the rod and not to the inside of the metal connector.
When the assembled rod is pulled in tension in its threaded ends, the solid adhesive wedges bonded to the rod press against and force against the annular wedges. Slippage which occurs between the rod body and the end fitting causes the larger end of the adhesive wedge to separate from the surface of the metal leaving a slight gap.
A compressive force is imparted to the rod itself as the metal connector and the adhesive wedge press against each other to resist any further slippage. This force of compression is applied across the entire interval where the adhesive wedge and the metal surface contact. No compression force is applied in the segment adjacent the gap.
The abrupt change at the end of the gap from no compression to full, heavy compression results in a concentration of shear stress at that point, leading to the possibility of failure in the rod.
Accordingly, there exists a need to design a wedge or annulus that will spread out the force of compression along the annulus and eliminate the concentration of shear stress at a particular point in the annulus.
It is, therefore, a principal object and purpose of the present invention to provide an end fitting for a cylindrical rod or cylindrical wire that will spread out the force of compression along the adhesive and rod within the receptacle of the end fitting.